Animals have different ways of surviving winter in locations like Michigan where temperatures fall below freezing and the usual food sources are scarce or absent. Some (especially birds and mammals) find sufficient food options and remain active all winter. Some (especially insect-eating birds) migrate to a warmer climate for the season. Some (especially insects) survive only in the egg or pupa stage that will grow into the next generation of adults in the spring. And some hibernate.
I am using the term “hibernation” here to mean an adult remaining in an inactive or dormant condition, in the same sheltered location, all or most of the winter. Mammals (such as bears or groundhogs) may be the hibernators that we think of first, but many “cold-blooded” animals like reptiles, amphibians, insects, and crustaceans also hibernate.
On a recent walk, I started thinking of species that I find every year in Eliza Howell Park that are now hibernating. They include these six.
While tree squirrels remain active all winter, often relying on the food (especially nuts) that they stored in the fall, the chipmunk, the only ground squirrel in EHP, hibernates. It stores some food for the winter in its winter burrow and eats when it awakens from time to time during the winter, before returning to its dormant winter condition. It will emerge in the spring, when I often see the first of the year near the path by the river on a sunny day.
2. Common Garter Snake
I was walking in the park in the afternoon on December 2 this year when I was surprised to see a Garter Snake. My first thought was “I thought you would be hibernating.” They usually are in their den well before December, but this was a warm day (68 degrees), so it may not have been quite ready to settle down for the winter.
The non-venomous Garter Snake, with its three stripes along its roughly 2 feet length, is the only snake species that I encounter with any regularity in Eliza Howell Park.
Photo by Margaret Weber
The Mourning Cloak is the first butterfly species I expect to see in the spring. Different from almost all other butterflies in our region, it overwinters as an adult rather than in a developing stage or by migrating – and this is the explanation for its early emergence. It finds a hidden location, such as under bark, seeking protection from the birds that forage for insect life all winter. The location may not protect it from freezing temperatures, but it can survive them.
In early October, these (Brown-lipped?) land snails were common in the wild flowers, climbing plants to consume dying leaves. Around first frost they settle down for the winter. They use their mucus to close the shell mouth and protect themselves from the cold. Before they seal themselves in, they find a location under rocks or ground litter protected from the cold and stay there until it is time to emerge in the spring. (Note “The Snails Have Returned,” April 18, 2018.)
This picture, taken in June, is of a half-grown immature Groundhog. Adults mate shortly after they emerge from hibernation in the spring. Groundhogs use burrows throughout the year, but they sometimes dig a separate one for the winter. They settle in below the frost line, rely upon their stored body fat, and sometimes lose half their weight during the months of winter. I don’t know if any of the Eliza Howell groundhogs check the weather on February 2, but, if one does, no one is there watching.
Except for gathering at the breeding pond for an intense couple of days in April (See “American Toad Breeding Pond,” July 23, 2018), adult American Toads live quite solidary and nocturnal lives. In the Fall, they dig winter burrows with their feet, sometimes up to three feet deep. When the weather begins to warm and the insects become more active, they emerge and soon after, when the air temperature and the body temperature are right, the males will head to the breeding pond and call the females. (Some of us toad watchers will be listening.)
While the dates vary somewhat, I usually see each of these species for the first time in April. Until then, I wish them a peaceful winter.